“Charging” devices are used in combustion engines, in order to increase the engine specific power output, which is directly proportional to the rate of air flow. In addition to the dynamic boost that utilizes the dynamics of the air drawn in, in some cases a mechanical charging design are used, where the Supercharging device is driven directly by the engine. In other charging device designs, Turbochargers typically include a compressor wheel to boost air that is drawn into the engine and a turbine wheel which is driven by the engine exhaust. In turbocharger designs, due to exhaust temperatures as high as 1050 degrees Celcius, associated components need to withstand temperatures which may exceed 500 degrees Celsius. Where a exhaust turbine drives a compressor for boosting inlet pressure to an internal combustion engine (e.g., as in a turbocharger), a wastegate at the turbine wheel housing provides a means to control the boost pressure. The turbine wastegate allows some exhaust to bypass the turbine and transfer such exhaust to the atmosphere.
An internal wastegate may be integrated at least partially into a turbine housing. An internal wastegate typically includes a flapper valve (e.g., a plug), a crank arm, a shaft or rod, and an actuator. A plug of a wastegate often includes a flat disk shaped surface that may seat against a flat seat (e.g., a valve seat or wastegate seat) disposed about an exhaust bypass opening defined in the turbine wheel housing. However, though various plug designs may include a protruding portion that extends into an exhaust bypass opening (e.g., past a plane of a wastegate seat).
In a closed wastegate duct position, a wastegate plug should be seated against a wastegate seat (e.g., seating surface) with sufficient force to effectively seal an exhaust bypass opening (e.g., to prevent leaking of exhaust from a high pressure exhaust supply to a lower pressure region). Often, an internal wastegate is configured to transmit force from an arm to a plug (e.g., as two separate, yet connected components). During engine operation, load requirements for a wastegate vary with pressure differential. High load requirements can generate high mechanical stresses in a wastegate's kinematics components, a fact which has led in some instances to significantly oversized component design to meet reliability levels (e.g., as demanded by engine manufacturers). Reliability of wastegate components for gasoline engine applications is particularly important where operational temperatures and exhaust pulsation levels can be quite high.
Accordingly, a need has developed to provide a wastegate actuator assembly which may withstand the high exhaust temperatures and the high exhaust pulsation levels over an extended period of time.